The following correction was printed in the Observer's For the record column, Sunday October 21 2007

Contrary to the article below, Quorn products are not suitable for vegans as they contain egg white. The same piece recommended soya milk as a source of vitamins D and B12, but these are only found in fortified soya milk. Vitamin B2 and not, as we said, B12, is present in wheat germ, yeast extract and avocado.

Question

I'm a 55-year-old mother, and my 17-year-old son has just announced that he wants to become a vegan. He's been inspired by his girlfriend, who is an ardent animal-rights supporter. She has been a vegetarian for five years and now wants to cut out fish and dairy products. While I applaud their ethics, I'm really worried that if my son chooses this way of eating, he will be more prone to colds and become even thinner and paler than he already is. As he hopes to go to university next year and I will no longer be able to keep an eye on him, I'd really like to teach him what to cook for himself and to know whether there are any supplements he should take to stay healthy. Can you help?

· If you have a health question for our experts, email health@observer.co.uk

The dietician
Jacqui Lowdon

For optimum nutrition, a vegan diet should contain two or three protein foods and cereals, vegetables, fruits and fats daily. Soya (including soya milk), Quorn, beans, pulses and nuts contain protein.

All vegetable sources offer lower levels of protein than those found in fish and meat, so devise meals with pulse and cereal combinations to maximise his intake - for example, beans on toast, mixed bean and rice salad, bean soup and bread, or lentil burgers on a wholemeal bun.

Soya milk and cereals are rich in vitamins D and B12; wholegrain cereals and breads provide iron and essential fatty acids, with green leafy veg adding iron, calcium and B12. Calcium is also found in legumes, cashew nuts and almonds; iron is found in pulses, tofu, nuts and Quorn, and B12 is found in wheat germ, yeast extract and avocados. Your son's diet should also include plenty of oils, nuts and seeds for essential fatty acids.

· Jacqui Lowdon is a spokesperson for the British Dietetic Association

The chef
Barry Baker

Vegan meals lend themselves to meze or tapas-style menus - a number of smaller dishes and lots of ingredients. Cultures that use much less meat and dairy than ours favour this style of eating and know how to use spices to make the most of vegan ingredients. It is ideal for students, too, because so much can be bought ready made. Turkish, Indian, Italian, Spanish, Middle Eastern and Japanese delis and corner shops will have suitable delicacies.

Experiment by mixing raw and cooked, spicy and pickled foods, and use exotic fruit and vegetables. Hummus is delicious with Japanese rice crackers, and stir-frys are simple to cook at home. Add a sachet of salsa or satay sauce, or make your own sweet and sour sauce by reducing ketchup, sugar, orange juice and vinegar over a low heat. Add beans, chickpeas and tofu for protein, and fresh coriander or basil for taste. Serve with rice, couscous or flatbread.

· Barry Baker is head chef at Henderson's vegetarian restaurant in Edinburgh

The supplements specialist
Dirk Budka

The key nutrients likely to be lacking in a vegan diet are iron, iodine, zinc, calcium, and vitamins B2 and B12. Where they are found in vegan foodstuffs, they may be in a form difficult to absorb; for example, only approximately 10 per cent of the iron in spinach, beans or lentils is absorbed by the human gut, compared with 50 per cent or more of the iron in liver.

This is why supplements are helpful. Take a good vitamin supplement for riboflavin (B2) and B12. A daily zinc supplement (15mg) and a calcium-magnesium pill (calcium 600-1,000mg, magnesium 300-600mg) boost immunity. Kelp is a good iodine supplement: your son should take it daily, but since too much iodine has been linked to thyroid problems he should have his thyroid function tested annually through his GP. A yearly test for iron levels is essential, too, because too much iron has been linked to heart and brain damage, diabetes and Parkinson's disease.

· Dirk Budka is a microbiology and immune-biology specialist at the Hale Clinic of complementary medicine